Research has been conducted on a means for improving the quality of a transmission channel or extending a transmission channel in order to increase a data transmission capacity in a wireless communication system. As one of various means for improving the quality of a transmission channel and increasing a transmission capacity, there is a scheme capable of transmitting an even larger amount of data at one time over the same transmission channel by improving a Signal to Interference and Noise Ratio (SINR), which is a parameter for indicating the quality of the transmission channel.
The concept of the SINR scheme as described above is expressed by Equation 1 below.
                    SINR        =                              p            serv                                                              ∑                i                            ⁢                                                          ⁢                              I                                  OS                  ⁡                                      (                    i                    )                                                                        +            Noise                                              [                  Eqn          .                                          ⁢          1                ]            
where Pserv represents the strength of a signal received from a serving Base Station (BS) to a Mobile Station (MS). IOS(i) represents the strength of an interference signal that the MS received from the ith interference cell (i.e. other cells/sectors). Noise represents the strength of a noise among the received signals.
Therefore, the quality of the transmission channel can be improved when the strength of a received signal is increased by reducing the strength of an interference signal received from each interference cell, or by increasing the strength of a transmission signal from a serving BS. As the SINR is improved, a larger amount of data may be transmitted over the improved transmission channel.
Meanwhile, a Spatial Multiplexing (SM) technology can be used as a means for extending the transmission channel. It signifies the technology of generating an additional transmission space or layer by using a multi-antenna technology and then increasing a data transmission capacity through the generated additional transmission space or layer for the same time-frequency space.
When the SM technology is used, there is an advantage due to the extension of the additional transmission space or layer although an additional frequency use is added to the same time-frequency space. Due to the additional frequency use, a self-interference Iself is additionally generated. An SINR including self-interference Iself is expressed by Equation 2 below.
                    SINR        =                              p            serv                                              I              self                        +                                          ∑                i                            ⁢                                                          ⁢                              I                                  OS                  ⁡                                      (                    i                    )                                                                        +            Noise                                              [                  Eqn          .                                          ⁢          2                ]            
As can be seen in Equation 2, the SM technology is unavoidably associated with an additional self-interference Iself, when data is transmitted. Accordingly, the SM technology is effective when other sector interferences IOS(i), which are interferences from other BSs (i.e. interference cells), are small or a strength Pserv of a received signal with respect to a self-BS (i.e. a serving BS) is large.
Meanwhile, uplink wireless communication from a MS is different from that of downlink wireless communication from a BS because transmission power of a MS is limited, and also because power should be split for each antenna and a split power should be transmitted to each MS. In this regard, the SM technology has limits on its use.
Accordingly, in order to increase a transmission capacity while overcoming the limit of the transmission power of the MS, use is made of multi-user CSM (Collaborative Spatial Multiplexing), in which for an uplink, it is not a single MS that transmits data to the uplink but at least one MS is allocated to the same resources.
Also, when the multi-user CSM technology is used, similarly to when the SM technology is used, as other sector interferences IOS(i) (which are interferences from other BSs) is reduced or as the signal strength Pserv of a self-BS is increased, the performance of the multi-user CSM improves. Additionally, in a receiver, an additional internal radio wave interference is added, and therefore, self-interference (or interference between layers) Iself occurs. Hence, the receiver needs to properly control the occurrence of the self-interference.